Charged particles cannot travel faster than the speed of light, as is known by Einstein's Special Relativity theory. However, a pattern of electric polarization can travel faster than the speed of light by a coordinated motion of the charged particles. Experiments performed at Oxford University and at Los Alamos National Laboratory established that polarization currents can travel faster than the speed of light. Two rows of closely-spaced electrodes were attached on opposite sides of a strip of dielectric alumina. At time t, a voltage was applied across the first pair of opposing electrodes to generate a polarization current in the dielectric alumina. A short time later, t+delta t, a voltage was applied to the second, adjacent pair of opposing electrodes, whilst the voltage applied to the first electrode pair was switched off, thus moving a polarization current along the dielectric. This process continued for multiple pairs of electrodes arranged along the dielectric. Given the sizes of the devices, superluminal speeds can be readily achieved using switching speeds in the MHz range. More subtle manipulation of the polarization current is possible by controlling magnitudes and timings of voltages applied to the electrodes, or by using carefully-phased oscillatory voltages. The superluminal polarization current emits electromagnetic radiation, so that such devices can be regarded as antennas. Each set of electrodes and the dielectric between them is an antenna element. Since the polarization current radiates, the dielectric between the electrodes is a radiator element of the antenna.
Superluminal emission technology can be applied in a number of areas including radar, directed energy, communications applications, and ground-based astrophysics experiments.
It is desirable to build such a system using a modular approach with identical antenna elements closely spaced along a line or along a curve designed to give a desired, quasi-continuous trajectory in the dielectric for the polarization current. Previously designed modular antenna elements had a coaxial cable connected to each antenna element. For each antenna element, the inner conductor of the coaxial cable was connected to the electrode on one side of the dielectric radiator element and the outer conductor (ground) to an electrode on the other side of the dielectric. The application of a voltage signal to such a connection establishes an electric field across the dielectric radiator element and hence creates the polarization. The connection to ground is straightforward due to the accessibility of the outer conductor. However, the inner conductor requires careful shaping to establish a smooth change in impedance. Moreover, a relative height of the outer conductor to the inner conductor proved difficult to replicate for each antenna element. Given the manufacturing tolerances, small variations in the relative heights of the conductors resulted in wide performance variations. In addition, a concentric conducting tube was provided around the coaxial cable to act as a quarter-wave stub. However, in the original embodiment it was found that the performance of the quarter-wave stub was very susceptible to slight variations in manufacturing tolerance, leading to large variations in performance from almost identical elements. This is clearly undesirable for antenna applications.